Microminiaturized electrostatic pump

ABSTRACT

An electrostatic pump includes two electrodes, which are spaced apart essentially in the pump flow direction and which are adapted to have applied thereto a potential for injecting an ion current flowing between the two electrodes. For further microminiaturization of the pump, the pump includes two semiconductor components, which are arranged one on top of the other in the pump flow direction and which are so structured that the electrodes form an integral constituent part of the semiconductor components.

FIELD OF THE INVENTION

The present invention relates to a microminiaturized electrostatic pump,and more particularly to a microminiaturized electrostatic pump havingtwo electrodes in a non-conductive fluid which are spaced apart in thepump flow direction, the electrodes having applied thereto a potentialfor injecting or for accelerating an ion current which flows betweensaid electrodes through the fluid.

BACKGROUND OF THE INVENTION

Electrostatic pumps operating without any moving parts have been knowne.g. from U.S Pat. No. 4,634,057, from U.S. Pat. No. 3,398,685, as wellas from U.S. Pat. No. 4,463,798 for a fairly long time. Suchelectrostatic pumps have at least two electrodes spaced apartessentially in the pump flow direction, the fluid (liquid or gas) to bepumped flowing around the electrodes. The electrodes are adapted to haveapplied thereto a d.c. potential or an a.c. potential so as to inject anion current flowing between the electrodes through the fluid. The gasesor liquids which are adapted to be pumped by means of an electrostaticpump are media, which are essentially non-conductive and which normallyhave a resistance value in the order of 10⁷ to 10¹⁰ ohm cm. The ionsinjected into the fluid by the electrode, which is normally providedwith a sharp tip, run through the fluid upon moving to the oppositeelectrode. This relative movement of the ions in the fluid to be pumpedproduces the pumping action of such an electrostatic pump, which,consequently, is capable of functioning without any moving parts.

Typical electrostatic pumps according to the prior art, which isestablished, e.g., by U.S. Pat. No. 4,463,798 or by U.S. Pat. No.4,634,057, consist essentially of a tubular housing member, which isconstructed such that a fluid can flow therethrough in the axialdirection and which is provided with a first centrally arrangedelectrode in the form of a cone tip arranged at an axial distance fromthe counter-electrode, such distance being normally adjustable by meansof a thread, and the counter-electrode consisting essentially of anozzle provided with a recess in the form of a truncated cone. Thetypical housing member of the known electrostatic pumps is made ofplastic material. The electrodes, which consist of metal, are normallyscrewed into the housing member. The known electrostatic pump having thestructure described not only requires comparatively high operatingvoltages in the order of 15 kV to 40 kV, but it also requires acomplicated adjustment in order to set an appropriate electrode spacing.In addition, the structural design of the known electrostatic pumpprecludes any far-reaching miniaturization of such pump so that thepossible fields of use of the known electrostatic pump are restricted.

U.S. Pat. No. 3,267,859 disclosed an electrostatic pump provided with acylindrical housing of plastic material having arranged therein twospaced metal electrode plates whose electrodes have a web-shaped oredge-shaped cross-sectional configuration. This pump is not suitable forthe purpose of microminiaturization.

OBJECT OF THE INVENTION

It is the principal object of the present invention to provide amicrominiaturized electrostatic pump, which is further miniaturizedbeyond what has been known before.

SUMMARY OF THE INVENTION

The foregoing object is achieved by providing two semiconductorcomponents, which are arranged one on top of the other essentially inthe pump flow direction, and which are so structured that the electrodesform an integral constituent part of the semiconductor components.

The present invention is based on the finding that the complicatedstructure of an electrostatic pump, which is disclosed in the prior artand which is opposed to further miniaturization, as well as theelectrode adjustment problem can be avoided by composing theelectrostatic pump of two semiconductor components, which are arrangedone on top of the other in the pump flow direction and each of which isstructured such that the electrodes define an integral constituent partof the semiconductor components. A microminiaturized electrostatic pumpconstructed in accordance with this teaching of the present inventioncan be produced by the high-precision photolithographic etching methods,which are known in the field of semiconductor technology. Due to thefact that the electrodes are formed integrally with the semiconductorcomponents, a very far-reaching miniaturization is possible so that theinvented microminiaturized electrostatic pump is also suitable for newfields of use, such as the integration into micromechanical structuralunits. As one example where such an integration into micromechanicalstructural units is used, the invented microminiaturized electrostaticpump is used as a heat pump for cooling electronic components. In viewof the fact that, by means of photolithographic processes,semiconductors can be structured with accuracies below the micrometerrange, this structural design of the invented microminiaturizedelectrostatic pump permits an adequate high-precision fixation of thetwo electrodes relative to each other, so that even in the case of verylow operating voltages the electrodes will be able to reliably maintainthe very small mutual distance which will then be necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be explained indetail hereinbelow with reference to the appended drawings, in which:

FIG. 1 shows a perspective view, part of which is a sectional view, of asemiconductor component forming a constituent part of an embodiment ofthe pump according to the invention.

FIGS. 2 to 7 show cross-sectional representations of various embodimentsof the electrostatic pump according to the present invention.

DETAILED DESCRIPTION

FIG. 1 shows one of the two semiconductor components, which arecontained in a first embodiment of an electrostatic pump according tothe present invention. This semiconductor component is a single-crystalsilicon semiconductor component, which is provided with referencenumeral 10 in its entirety. This silicon semiconductor component 10 ispreferably n+-conductive, but said component 10 may also be providedwith doped epitactical or diffused areas. In the embodiment shown, thesingle-crystal silicon semiconductor component 10 has a (100) crystalorientation. On the front of the silicon semiconductor component 10, aninsulating layer 11 is provided, which has a front recess 11a in atleast one flow-through region. The single-crystal silicon semiconductorcomponent is additionally provided with a rear recess 11b, which alsoextends at least over the flow-through region. In the area between frontrecess 11a and rear recess 11b, the single-crystal silicon component isprovided with a grid-shaped electrode 13 having a plurality ofprism-shaped pits 12 which define the flow-through region. Thegrid-shaped electrode 13 is an integral component of the siliconsemiconductor component 10.

The structure of the silicon semiconductor component 10 described aboveis produced by manufacturing techniques in the field of semiconductortechnology which are known per se, in a photoetch process. For thispurpose, the still unstructured single-crystal silicon semi-conductorcomponent 10 has first deposited thereon the electric insulating layer11. In the preferred embodiment, this is done by depositing a Pyrexglass layer on a thermally produced silicon dioxide layer by means ofcathode sputtering. The recess 11a is opened on the front side by anysuitable method. In the embodiment shown in FIG. 2, an area 24 issimultaneously opened on the front side, area 24 being later providedwith an ohmic contact to the silicon semiconductor component 21.

Subsequently, the silicon semiconductor component, which has beenstructured to the above-described extent, has applied thereto throughoutits whole surface a layer, which is resistant to alkaline etchingsolutions, and which may, for example, consist of silicon nitride, suchlayer being applied to the front and to the back of siliconsemiconductor component 10. This layer serves as an etch stop mask andwithin the previously opened area of the front recess 11a it isphotolithographically structured by conventional methods. Subsequently,an anisotropic etching process takes place, in the course of which theprism-shaped pits 12 are produced. If grid-shaped electrode structures13 with steeper edges are desired, isotropic etching processes may beused as well. In the case of the preferably used anisotropic etchingprocess employed for producing the structure of the grid-shapedelectrode 13 shown in FIG. 1, a 30% KOH solution is used as an etchingsolution. Depending on the desired thickness of the grid-shapedelectrode 13 produced later, the depth of the prism-shaped pits 12 isbetween 1 μm and 200 μm. The front of the structure now has appliedthereto an additional etch stop layer throughout its whole surface, andsuch layer can again consist of silicon nitride. Subsequently, after anadequate photolithographic treatment, the rear recess 11b is etched inan anisotropic etching process to such an extent that the lower areas ofthe prism-shaped pits 12 are reached, whereby the grid-shaped electrodestructure of electrode 13 is obtained. Residues of the etch stop layer(not shown) are now removed, a thin oxide film, which has formed on thesilicon, is removed, and the grid-shaped electrode 13 is then providedwith a metallic coating by conventional methods.

Depending on the intended use of the invented electrostatic pump, thesize of the recesses 11a, 11b and consequently, the size of the gridarea 13 is between approximately 0.1 mm×0.1 mm and approximately 10mm×10 mm. Typical sizes of the openings of the grid, which are definedby the prism-shaped pits 12, lie between 1 μm×2 μm and 1 mm×1 mm.

Deviating from the grid-shaped structure of the electrode 13 shown inFIG. 1, the electrode 13 can have a strip-shaped or web-shapedstructure.

In another embodiment variation from the embodiment shown in FIG. 1,cone tips (not shown) produced by deposition methods can be arranged atthe points of intersection of the grid-shaped electrode 13, whereby itis possible to achieve a concentration of ion injection at specificpoint areas in comparison with the ion current distribution which can beproduced by means of the grid-shaped electrode 13.

FIG. 2 shows a cross-sectional representation of an additionalembodiment of the microminiaturized electrostatic pump according to thepresent invention. This embodiment comprises two semiconductorcomponents 20, 21, which are arranged one on top of the other in thepump flow direction and each of which includes respective grid-shaped orweb-shaped electrodes 26, 27 opposed to each other essentially in thepump flow direction. In this embodiment, which is essentially formed byfitting together two semiconductor components of the type shown in FIG.1, two respective electrodes 26, 27 of the semiconductor components 20,21 are positioned essentially on one level with the front sides of thesemiconductor components 20, 21 and they are arranged in spacedrelationship with the reverse sides of said semiconductor components 20,21. The two semiconductor components 20, 21 are preferablyinterconnected by connecting, with the aid of electrostatic bonding, thereverse side of the upper semiconductor component 21 to the Pyrex glasslayer forming the insulating layer 22 of lower semiconductor component.In this embodiment and the embodiments which follow hereinafter, otherconnecting methods, such as wafer bonding or gluing, may be usedalternatively. In the embodiment according to FIG. 2, the distancebetween the grid- or web-shaped electrodes 26, 27 essentiallycorresponds to the thickness of the starting material, i.e. theuntreated single-crystal silicon semiconductor component.

Deviating from the embodiment according to FIG. 2, the grid-shapedelectrode 13 can be etched back from the front side of the semiconductorcomponent 20, 21.

In the embodiment of the electrostatic pump shown in FIG. 2, the uppersemiconductor component 21 is connected to a cover member 28 in the areaof its insulating layer 23, said cover member 28 including one or aplurality of outlet nozzles 29.

The embodiment of the electrostatic pump is shown in FIG. 3 differs fromthe FIG. 2 embodiment essentially insofar as the two semiconductorcomponents 30, 31 are here interconnected on their front sides in thearea of their respective insulating layer 32. The electrodes 33, 34 arehere etched back relative to the front sides of the semiconductorcomponents 30, 31, and this means that the mutual distance of the twoelectrodes 33, 34 is determined by the extent of etching back as well asby the thickness of the insulating layer 32. It follows that, in thisembodiment, the grid distance between the electrodes 33, 34, or the webdistance in cases in which a web-shaped electrode is chosen, can beadjusted on the basis of the extent of etching back relative to thefront side and on the basis of the thickness of the insulating layer 32.

The further modification of the electrostatic pump shown in FIG. 4,which comprises two semiconductor components 40, 41 interconnected inthe area of the front insulating layer 42, differs from the embodimentaccording to FIG. 3 only insofar as one electrode 43 of the twoelectrodes 43, 44 has a web width of the web structure or of the gridstructure which is so narrow that, due to the lateral under-etching ofthe etch stop layer, an edge-like electrode 43 is formed, whichparticularly promotes the injection of ions into the fluid due to thehigh field strength at the edge.

The embodiment of the electrostatic pump shown in FIG. 5 differs fromthe embodiment according to FIG. 4 essentially insofar as a thirdsemiconductor component 51 with an insulating partition 55 is providedbetween the two semiconductor components 50, 52 with the associatedstrip-shaped or web-shaped electrodes 53, 54, which are set backrelative to the respective front side of the semiconductor component,insulating partition 55 having formed therein flow-through openings 57only in the area of the opposed web-shaped electrodes 53, 54. Thisembodiment preferably includes the feature that, in the area of itsinsulating layer 56, the first semiconductor component 50 has its frontside connected to the reverse side of the third semiconductor component51 by means of electrostatic bonding. In the area of the insulatingpartition 55, said third semiconductor component 51 is connected to thefront side of the second semiconductor component 52 again by means ofelectrostatic bonding.

A more strongly modified embodiment of the invented microminiaturizedelectrostatic pump will now be explained with reference to FIG. 6. Inthis embodiment, one component 61 of the two semiconductor components60, 61 has an edge-shaped spacer 62, which comes into engagement with agroove 62a of the other semiconductor component 60. Furthermore,semiconductor component 61 is provided with an edge-like injector 63.The other semiconductor component 60 is provided with an essentiallyV-shaped opening 64, which is located in the area of the edge-likeinjector 63 of semiconductor component 61 and which maintains, in thearea of the injector 63, such a distance between the two semiconductorcomponents 60, 61 that a flow-through gap 64-65 of reduced width isdefined. On its side facing said one semiconductor component 61, theother semiconductor component 60 is covered with an insulating layer 67,which extends not only over the groove 62a but also over an essentialpert of the V-shaped opening 64 so that the opposed electrodes aredefined on the one hand by the tip of the edge-like injector 63 and onthe other hand by the border areas of the opening 64 of the othersemiconductor component 60, such border 10 areas being located adjacentthe tip.

In the area of the flow-through gap between the injector 63 and theopening 64 of the two semiconductor components 60, 61, a groove-shapedor gap-shaped inlet nozzle 65 is provided. With the exception of thearea of engagement at the location of the spacer 62, the twosemiconductor components 60, 61 are spaced apart by a free space 66.

The embodiment shown in FIG. 7 differs from the embodiment of FIG. 6essentially insofar as an insulating body 77 is arranged between the twosemiconductor components 70, 71. One of the two semiconductor components71 engages via its spacer 72 a groove 72a of the insulating body 77,thus defining by this fixed position a free space 76 between theinsulating body 77 and semiconductor component 71. In conformity withthe previously described embodiment, also the present semiconductorcomponent 71 is provided with an edge-like injector 73 defining togetherwith a V-shaped opening 74a of the insulating body 77 a flow-through gap74-75, which terminates in the area of a groove-shaped inlet nozzle 75of the semiconductor component 71. The other semiconductor component 70is provided with a V-shaped opening 74 located above the opening 74a ofthe insulating body 77 and defining acute-angled electrode edge portions78, which form the counter-electrodes to the edge-shaped injector 73.

For operating the electrostatic pump, the semiconductor components 20,21; 30, 31; 40, 41; 50, 51; 60, 61; 70, 71 are respectively connected toa d.c. source via ohmic contacts (cf. reference numerals 24, 25according to FIG. 2) so that an electric potential difference betweenthe two electrodes is created, such electric potential difference beingsufficient to inject ions into the fluid (gas or liquid) to be pumped.

ALTERNATIVE EMBODIMENTS

It is readily apparent that, for increasing the quantity delivered bythe pump according to the present invention, several pump components ofthe type shown in FIG. 2 to 7 may be connected in parallel. Furthermore,it is also possible to connect several pumps of this type in series, ifthis should be desirable for reasons of increased pressure. And it isequally possible to arrange more than two semiconductor components, oneon top of the other, instead of a series connection of pumps.

Instead of the preferably used semiconductor material silicon, all othersemiconductor materials can be used as a starting material as well.

Each of the embodiments shown can be provided with additional inlet andoutlet nozzles, although this is only shown in the case of theembodiments according to FIG. 2, 6 and 7.

Finally, the invented pump can also be employed for generating a staticpressure so that the term "pump", which has been used in the presentconnection, is intended to comprise also cases of use in which a fluidwithout any fluid flow only has to have pressure applied thereto.Furthermore, the term "pump" as used in the present application is alsointended to cover any means used for accelerating or for decelerating afluid flow.

What is claimed is:
 1. A microminiaturized electrostatic pump includingtwo electrodes (13; 26, 27; 33, 34; 43, 44; 53, 54; 63, 68; 73, 78),which are arranged in a essentially non-conductive fluid to be pumpedand which are spaced apart essentially in the pump flow direction, saidelectrodes being adapted to have applied thereto a potential forinjecting or for accelerating an ion current which flows between saidelectrodes through said fluid, and further including two components (10;20, 21; 30, 31; 40, 41; 50, 52; 60, 61; 70, 71), which are arranged oneon top of the other essentially in the pump flow direction and which arestructured by etched openings in such way that the electrodes form anintegral constituent part of said semiconductor components;characterizedin that components (10; 20, 21; 30, 31; 40, 41; 50, 52; 60, 61; 70, 71)and the electrodes (13; 26, 27; 33, 34; 43, 44; 53, 54; 63, 68; 73, 78)consist of a semiconductor material, the main surfaces of saidcomponents (10; 20, 21; 30, 31; 40, 41; 50, 52; 60, 61; 70, 71) extendat right angles to the pump flow direction, and the etched openings (12)extend through the components in the pump flow direction at both sidesof each electrode.
 2. A microminiaturized electrostatic pump accordingto claim 1,characterized in that the electrodes (13; 26, 27; 33, 34; 43,44; 53, 54; 63, 68; 73, 78) consisting of a semiconductor material areprovided with a metallic coating on their surfaces.
 3. Amicrominiaturized electrostatic pump according to claim 1,characterizedin that the electrodes (26, 27) of both semiconductor components (20,21) are respectively positioned on one level with the front side of saidsemiconductor components (20, 21) and are respectively arranged inspaced relationship with the reverse side of said semiconductorcomponents (20, 21) and that the semiconductor components (20, 21) arearranged in such manner that the reverse side of one semiconductorcomponent (21) is connected to the front side (22) of the othersemiconductor component (20).
 4. A microminiaturized electrostatic pumpaccording to claim 1,characterized in that the electrodes (33, 34; 43,44; 53, 54) of both semiconductor components (30, 31; 40, 41; 50, 52)are arranged in spaced relationship with the front sides of saidsemiconductor components, and that said semiconductor components havetheir respective front sides interconnected.
 5. A microminiaturizedelectrostatic pump according to claim 1,characterized in that thesemiconductor components (20, 21; 30, 31; 40, 41; 50, 51, 52; 60, 61;70, 71) are glued together.
 6. A microminiaturized electrostatic pumpaccording to claim 1,characterized in that an insulating body (77) isarranged between the two semiconductor components (70, 71), that one(71) of the two semiconductor components (70, 71) is provided with aspacer (72) and with an edge-like injector (73), that the insulatingbody (77) is provided with an essentially V-shaped opening (74a)defining together with said edge-like injector (73) a flow-through gap(74-75), and that, in the area of the essentially V-shaped opening (74a)of the insulating body (77), the other semiconductor component (70)defines at least one counter-electrode (78) cooperating with saidedge-like injector (73).
 7. A microminiaturized electrostatic pumpaccording to claim 1,characterized in that the semiconductor components(10; 20, 21; 30, 31; 40, 41; 50, 51, 52; 60, 61; 70, 71) have beenstructured by means of photoetch processes.
 8. A microminiaturizedelectrostatic pump according to claim 1,characterized in that theelectrodes (13; 26, 27; 33, 34; 43, 44; 53, 54; 63; 73) have aweb-shaped structure.
 9. A microminiaturized electrostatic pumpaccording to claim 8,characterized in that the web-shaped electrodes(26, 27; 33, 34; 43, 44) of the two semiconductor components (20, 21;30, 31; 40, 41; 50, 52) are arranged in essentially opposed relationshipwith one another.
 10. A microminiaturized electrostatic pump accordingto claim 1,characterized in that at least one of the electrodes (43; 53;63; 73) is triangular or wedge-shaped.
 11. A microminiaturizedelectrostatic pump according to claim 10,characterized in that the twosemiconductor components (50, 52) have arranged between them a thirdsemiconductor component (51) defining a partition (55) which extendsessentially at right angles to the direction of flow and which hasformed therein flow-through openings (57) only in the area of theessentially opposed web-shaped electrodes (53, 54).
 12. Amicrominiaturized electrostatic pump according to claim 1,characterizedin that the semiconductor components (20, 21) are interconnected byelectrostatic bonding.
 13. A microminiaturized electrostatic pumpaccording to claim 12,characterized in that at least one (20) of thesemiconductors components (20, 21) interconnected by electrostaticbonding is provided with a pyrex glass layer, which has been applied bycathode sputtering and which is provided in the area of connection withthe other semiconductor component (21).
 14. A microminiaturizedelectrostatic pump according to claim 1,characterized in that one (61)of the two semiconductor components (60, 61) is provided with a spacer(62) for engagement with the other semiconductor component (60) and withan edge-like injector (63), and that the other semiconductor component(60) is provided with an opening (64), which is essentially V-shaped incross-section and which defines together with the edge-like injector(63) a flow-through gap (64-65).
 15. A microminiaturized electrostaticpump according to claim 14,characterized in that the other semiconductorcomponent (60) is provided with an insulating layer (67), which coversthe side of said component (60) facing said semiconductor component (61)and which extends from said side over at least part of said essentiallyV-shaped opening (64).
 16. A microminiaturized electrostatic pumpaccording to claim 1,characterized in that the electrodes (13; 26, 27;33, 34; 43, 44) have a grid-shaped structure.
 17. A microminiaturizedelectrostatic pump according to claim 16,characterized in that thegrid-shaped electrodes (26, 27; 33, 34; 43, 44) of the two semiconductorcomponents (20, 21; 30, 31; 40, 41; 50, 52) are arranged in essentiallyopposed relationship with one another.
 18. A microminiaturizedelectrostatic pump according to claim 16,characterized in that theflow-through region of the semiconductor components (10) has an areafrom 0.1 mm×0.1 mm up to 10 mm×10 mm.
 19. A microminiaturizedelectrostatic pump according to claim 18,characterized in that themutual distance between the electrode webs of the electrode of the samesemiconductor component is in the range of from 2 μm to 1 μmm.
 20. Amicrominiaturized electrostatic pump according to claim 18,characterizedin that the distance between the opposed electrodes (26, 27; 33, 34; 43,44; 53, 54; 63, 68; 73, 78) of the two semiconductor components (20, 21;30, 31: 40, 41; 50, 52; 60, 70, 71) is between 5 μm and 500 μm.
 21. Amethod of producing a microminiaturized electrostatic pump including twoelectrodes (13; 26, 27; 33, 34; 43, 44; 53, 54; 64, 68; 73, 78), whichare arranged in an essentially non-conductive fluid to be pumped andwhich are spaced apart essentially in the pump flow direction, saidelectrodes being adapted to have applied thereto a potential forinjecting or for accelerating an ion current which flows between saidelectrodes through said fluid and further including two components (10;20, 21; 30, 31; 40, 41; 50, 52; 60, 61; 70, 71), which are arranged oneon top of the other essentially in the pump flow direction and which arestructured by etched openings (12) in such a way that the electrodesform an integral constituent part of the respective component, thecomponents being semiconductor components (10), the methodcomprising;applying a layer which is resistant to etching agents to oneside of the semiconductor component (10); photolithographicallystructuring with etch windows the layer which is resistant to etchingagents; and starting from the etch windows of the etchingagent-resistant layer, etching openings (12) through the semiconductorcomponent (10) thereby defining web-shaped or grid-shaped electrodes inthe pump flow direction.